Dust, lead particulate size

Dusts resuspended in localized atmospheres reflect both the distribution of lead species and particulate sizes in the dusts or soils serving as the source and the main mechanisms producing the resuspension. Street dusts have a bimodal distribution, the fine particle sizes arising from the tailpipes directly and the coarse materials from such mechanisms as smaller particle distribution. Al-Chalabi and Hawker (1997) reported that with increasing resuspension, the lead levels decreased, consistent with either coalescing small and coarser particles or increasing dispersion from the source. Similarly, Abu-Allaban et al. (2003) reported that road dust had most of its lead content in the coarse fraction. 

Attrition of particulate materials occurs wherever solids are handled and processed. In contrast to the term comminution, which describes the intentional particle degradation, the term attrition condenses all phenomena of unwanted particle degradation which may lead to a lot of different problems. The present chapter focuses on two particular process types where attrition is of special relevance, namely fluidized beds and pneumatic conveying lines. The problems caused by attrition can be divided into two broad categories. On the one hand, there is the generation of fines. In the case of fluidized bed catalytic reactors, this will lead to a loss of valuable catalyst material. Moreover, attrition may cause dust problems like explosion hazards or additional burden on the filtration systems. On the other hand, attrition causes changes in physical properties of the material such as particle size distribution or surface area. This can result in a reduction of product quality or in difficulties with operation of the plant. 

Dichlorobenzidine is not a volatile chemical. In the air, it may exist as dust particles or boimd to particulate matter. The absorption of 3,3 -dichlorobenzidine from such respirable particles into the body depends, in part, on the size of the particle. Large particles tend to deposit in the upper airways and are subsequently cleared by ciliary action with little absorption across limg tissues. However, the ciliary action transports the particles to the epiglottis where they are often swallowed, leading to gastrointestinal absorption. Smaller particles can penetrate more deeply into the respiratoiy tree, where 3,3 -dichloro-benzidine absorption may be significant. 

Candle filters have in general proved highly efficient, even for very fine particles of sizes down to the order of 1 pm. However, a number of problems remain to be solved, such as the build-up of dust cake on the filters leading to occasional cake bridging between candles, filter failure and breakage. A number of hot gas filtration systems have been developed and tested under industrially relevant conditions an advanced particle filter (APF) containing 284 candles was installed at the 70 MW (electric) Tidd PFBC demonstration plant at Brilliant, Ohio gas flow and particle deposition have been modelled by Ahmadi and Smith [53] for the Tidd filter vessel and by Mazaheri and Ahmadi [54] for the Siemens-Westinghouse particulate control device (PCD). 

Our eoneems with the induction and exaceibation of respiratoiy diseases encompass bronchitis, emphysema, asthma, and other nonoecupational diseases. (Pneumoconiosis and silicosis are eonsidered diseases due to occupational exposure, rather than to inhalation of ambient air.) The pollutants principally indicted are ozone, sulfur dioxide, nitrogen dioxide, suspended particulate matter, and mixtures of these pollutants. Concern over the effects of suspended partieulate matter on human health is particularly focused on what are called respirable or inhalable partieles, usually detined as particles less than 10 mn in size. Lead dust is the exeeption to the mle that particles must be inhaled to be hazardous to health. Lead... 

EPA, 2006). Reentrainment of lead in particulate back into the atmosphere from dusts and soils after initial deposition of lead from the atmosphere also occurs due to atmospheric mobilization (Cowherd et al., 1985 U.S. EPA, 2006). The range of lead transport via the atmosphere can be many miles for the smallest size particles to as short as meters for reentrained dust particles at roadways for heavy traffic or for large lead paint particles, as occurs with weathering and flaking of lead-painted surfaces in older buildings where particles are mobilized to nearby soil surfaces, around the drip line."... 

Dusts are technically defined as solids consisting of small particulate materials that in turn derive from a variety of materials through diverse processes of deterioration. While dusts can consist solid particulates of any size, those which both contain lead and arise from environmental transformations of lead sources are generally considered to have an average diameter of 50 pm. 

Techniques for sampling water are less complex than those for sampling air [77]. Filtering is an important consideration in water analysis, since lead can occur in the particulate fraction or in solution in aqueous samples. The preparation of soil and soil dust samples for lead analysis usually involves drying, homogenation by grinding, and sieving to obtain a particle size distribution. 

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